1. Field of the Invention
The present invention relates to a noise reduction apparatus and a noise reduction method which is used for audio reproducing system containing various types of audio components.
2. Description of the Related Art
A noise reduction technique is used for a tape deck in order to reduce hiss noise in sound. In this noise reduction technique, the level of the sound in middle and high frequency bands is compressed when recording, and the compressed sound is expanded when reproducing. In this manner, hiss noise contained in the sound from the tape can be reduced. However, this technique has a disadvantage that it is needed to compress the sound level when recording. That is, this noise reduction cannot be effected for the sound that is not compressed.
In recent years, there are various types of audio apparatuses, such as a CD (Compact Disk) player, a cassette desk, a tuner, an MD (Mini Disk) player, etc. Therefore, an audio reproduction system which contains these audio apparatuses as audio components and controls the reproduction of these audio components has been developed. In such an audio reproducing system, all the reproducing signals output from the audio components are passed through one common signal processing circuit, and then, these signals are sent to output devices such as speakers or the like.
In such an audio reproducing system, the noise reduction is needed in order to make sound clearer. However, as the audio reproducing system has different types of audio components, the different noise reduction circuit or device is needed for every audio component. Because, in order to reduce noise effectively, it is necessary to set parameters (e.g., a threshold level for cutting noise) of the noise reduction circuit or device in such a condition that these parameters are matched the level of the reproducing signal output from each audio component. The levels of the reproducing signals output from the respective audio components are different from each other. Therefore, a plurality of noise reduction circuits or devices are needed depending on the number of the types of audio components. As a result, the construction of the audio reproducing system becomes complex. In addition, if one common noise reduction circuit or device, whose parameters are set to match one of the audio components, is used, it is difficult to achieve optimum noise reduction for every audio components.